Glowworm Ultimate 50FF coming on - at off times. Any ideas?
My Glowworm boiler is flashing up even though the Honeywell ST699 control - a new unit - is off for both heating and hot water, i.e. both red indicator lights are off. This happens randomly, often after several hours of inactivity. In addition the pump is not stopping and there's a single orange neon illuminated inside the boiler control box. I am pretty sure the wiring is OK, because over the last two weeks the boiler has behaved itself. I don't think this boiler has a frost stat (and anyway the problems were happening over the summer) but could it be another stat., or the pcb or a faulty motorized valve? Or what? Last winter when the boiler was on for long periods of time, the pump (a Grundfos UPS 15-50) was occasionally making brief 'siren' noises. Could the pump be to blame?
Any help would be most welcome.